Did you make this instructable?

you can focus the sound a source emits, which will make it louder in certain places, but it's not actually amplifying anything... The only way you could do this would be to change the substrate... like, if you had a room and half the room was filled with regular air and the other half was filled with helium...

Yes. Intensity of sound is affected by frequency. Intensity is more with higher frequency. That's why high frequency sounds are used in SONAR etc since they have more energy and can reach back after reflection. Here is a link that could help you out:http://forums.studentdoctor.net/archive/index.php/t-649692.html Also you can amplify sound waves. Using an electronic circuit you can record the sound( microphone) and amplify it and then again using a speaker play the amplified sound. Otherwise by forcing the vibration on a body of larger surface area more air is put into motion thus there is more intensity. Hope this helps you. Thanks

The first part is actually not true, as kelseymh points out, frequency is not tied to energy in sound. If they were related, then high pitches would always be louder than low pitches which of course is not true. Also SONAR does not only use high frequencies. There are also mid and low frequency sonar. High frequency SONAR gives a much more detailed, finer result but is subject to much greater scattering. That's where mid- and low-frequency SONAR come in. They aren't as precise but they don't scatter as bad over long distances. Most SONAR systems use multiple frequencies at once.

It is a bit complicated. There is an inverse relationship between intensity and frequency, and a direct relationship on the acceleration on the particles (molecules) in the medium. To the naive reader, that relationship makes it look like higher frequency sounds are "less intense" than low frequency (the opposite of what "sigupta" wrote).

However, because the acceleration and frequency are related (high frequency means the pressure changes faster, and therefore the particles are being accelerated more), the two effects cancel out, and intensity fundamentally depends only on the absolute pressure difference (i.e., the amplitude).

I think the most common method used for amplifying sound waves is via electronics. That is to say the sound signal is converted to an electrical signal using a microphone. Then the electrical signal is amplified, using a device called (wait for it) an "amplifier". http://en.wikipedia.org/wiki/Audio_power_amplifier Then the amplified electrical signal can drive a speaker, which converts the electrical signal back into sound.

That's the usual trick if you want to amplify a sound signal with a wide range of frequencies, like human speech or music.

In contrast if you want to amplify just a single frequency, the device may end up looking like a resonator,http://en.wikipedia.org/wiki/Resonator or including a resonator in its construction.

In response to your question about power and frequency: the power carried by a sound wave does not depend on frequency. Power is proportional to the square of the amplitude, measured as sound pressure, or displacement.

It's sort of the same thing in the electrical domain. The power in a electrical signal is also proportional to the square of its amplitude, and for electrical signals, amplitude is measured in volts, or amperes.

Sound waves are macroscopic pressure variations in air (or water). They are not electromagnetic waves, and so they do not have the same quantum frequency-energy relationship. For sound waves, the energy carried depends on the amplitude (intensity), regardless of the frequency.